In this paper, we propose an iterative joint DA/DD channel estimation algorithm for known symbol padding (KSP) OFDM. The pilot symbols used to estimate the channel are not only located in the guard interval, but also on some or the OFDM carriers. Initially, the channel is estimated using the pilot symbols only. Next, a decision is made with respect to the transmitted data symbols. We consider both hard and soft decision of the data symbols. The decisions on the data symbols are then used to update the channel estimate in a joint DA/DD estimation algorithm. The algorithm iterates between data detection and channel estimation until convergence is reached. At high SNR, the MSE performance of the iterative estimator converges to the MSE performance of the case where all data symbols are prior known at the receiver, i.e. the all pilot DA estimator. It turns out that the MSE performance of hard decision of the data symbols reaches the MSE of the all pilot DA estimator at lower SNR than that of soft decision of the data symbols; this is caused by some approximations needed to simplify the estimation algorithm.